Russian Patent 2 072 135 presents a method for fire extinguishing wherein a gas and aerosol mixture is released when a pyrotechnic charge burns, the mixture reacting with the combustion products in the fire area and resulting in the fire being extinguished. Before being supplied to a protected area, the gas and aerosol mixture is cooled; for that purpose, the mixture is combined with substances that have a high heat-absorbing capacity and a high degree of degassing such as carbonates, hydrates, hydroxides, and oxalates, which are used in the form of pellets or tablets.
An apparatus for carrying out this method has a casing that contains a pyrotechnic composition, a heat protection layer, and a discharge port. A pyrotechnic composition is ignited by means of a standard igniter. The cooling of the gas and aerosol mixture that is released during burning of the pyrotechnic composition is carried out in a cooling unit that has a form of a container which is filled with a cooling medium and is located in the casing between the pyrotechnic composition and the discharge port.
A serious disadvantage of this method and apparatus lies in the fact that the combustion products of the pyrotechnic composition, which consists of 12% KClO.sub.4, 60% KNO.sub.3, 18% C.sub.3 H.sub.5 O, and 10% Mg, are highly toxic. Upon thermal decomposition of such pyrotechnic compositions, toxic gases--Cl.sub.2, NO, NO.sub.2, NH.sub.3, HCN, CO, and CH.sub.4 --are released.
The use of carbonates, hydrates, and oxalates as cooling media results in an additional increase in the concentration of toxic gases that are released when the cooling medium reacts with the hot gas and aerosol mixture. Thus CO.sub.2, CO, H.sub.2 O, and K.sub.2 CO.sub.3 are released upon decomposition of potassium oxalate--K.sub.2 C.sub.2 O.sub.4, and MgO, H.sub.2 O, and CO.sub.2 are released upon decomposition of magnesium carbonate MgCO.sub.3 .times.5H.sub.2 O. The water vapor that is released can react with chlorine, nitrogen oxides, and carbon dioxide to form acids--HCl, HNO.sub.3, H.sub.2 CO.sub.3 --which are also harmful for living organisms and for other objects present in the fire area.
For appropriate cooling of the gas and aerosol mixture, it is required that the above-mentioned substances have a mass that is equal to, or substantially greater than, the mass of the aerosol-forming mixture. This also results in an increased quantity of the toxic gases that are formed upon decomposition of the cooling medium.
Russian patent 2 101 504 presents a pyrotechnic composition that forms a gas and aerosol mixture, which comprises 67 to 72 percent by mass of potassium nitrate with a specific particle surface area of at least 1500 cm.sup.2 /g, 8 to 12 percent by mass of phenol-formaldehyde resin as a fuel binder, having a particle size that is not in excess of 100 .mu.m, the balance comprising a gas- and aerosol-forming substance, namely dicyandiamide, having a particle size that is not in excess of 15 .mu.m. The composition can also contain potassium carbonate, potassium benzoate, or potassium hexacyanoferrate in an amount of 4 to 12% by mass.
This pyrotechnic composition has the following disadvantages:
Low flame propagation velocity of the composition (about 2.4 mm/s), which causes a low extinguishing rate. The composition has a broad combustion temperature profile (from the condensing phase of the composition to the hottest point of the flame), whereby it is difficult to cool the gas and aerosol mixture. PA1 Low content by mass (no more than 64%) of the solid phase, which is the main component of the gas and aerosol mixture for fire extinguishing. PA1 Toxicity of the combustion products of the pyrotechnic composition. More specifically, although there is a low content of such gases as CO.sub.2 and NH.sub.3 in the combustion products, the problem of toxicity is not fully resolved, because the concentrations of products of incomplete oxidation such as CO, NO, HNC are rather high. PA1 Low efficiency of the process of complete oxidation of the products of incomplete combustion. The method is based on the use of the oxidizing gas that is taken from the ambient air by means of a jet. The concentration of oxygen that is taken from the air in a jet flow is not sufficient to ensure the complete oxidation of the gases that are formed when the composition burns. An increase in the oxygen concentration is only possible by raising the rate of ejection, which would require a greater size of the jet nozzle and a substantial increase in the gas and aerosol mixture flow velocity. This would cause an increase in the pressure within the combustion chamber, which would require a greater strength of the casing. PA1 Low efficiency of cooling of the combustion products with a liquid coolant by means of a known cooling system. Thus water and a coolant (a mixture of 40/60 of polyethylene glycol and water) is normally used, which has a boiling point over 100 to 130.degree. C. In addition, in order to ensure the effective cooling of the gas and aerosol mixtures that are released as a result of combustion from 800 to 100.degree. C., either a large heat exchange surface area is required, or the coolant flow velocity has to be high. In order to meet these requirements, a much larger metal container would be necessary, thus complicating the practical application of the device. PA1 burning a charge of a composition that generates an aerosol; PA1 cooling the resulting gas and aerosol mixture by causing it to pass through a heat-absorbent filling; PA1 completely oxidizing the combustion products by causing the cooled gas and aerosol mixture to pass through an oxidizer filling; PA1 feeding the gas and aerosol mixture to the fire area and extinguishing the fire. PA1 The above-mentioned catalysts in the gas and aerosol mixture generating composition or on the surface thereof have a catalytic effect on the reactions of decomposition of components that are present in the condensed phase of the composition but they do not have any practical effect on the reactions in the gas phase. The main result of the activity of these catalysts can only be deceleration or acceleration of decomposition of the components. As a result, the composition will burn either too slowly or too rapidly. This would not permit complete oxidation of the combustion products. PA1 The above-mentioned catalysts in the chemical coolants mainly affect the rate of decomposition. More specifically, decomposition of the pellets or tablets of the heat-absorbent charge may have a catalytic effect on the CO, NO, HCN, NH.sub.3 oxidation reactions. As a consequence of this, the gas temperature during the gas passage through the heat-absorbing charge decreases, thus lowering the efficiency of the complete oxidation. PA1 The efficiency of a special oxidizer filling that is located directly in front of the discharge port is also not very high. This is primarily because the gas and aerosol mixture at this point is already cooled. Since the velocity of flow through the oxidizer filling is high, the reaction of total oxidation is not completed. In order to enhance the efficiency of the complete oxidation, the oxidizer filling should be made thicker. This will result in lower discharge velocity and also in higher pressure build-up in the casing of the apparatus, which may cause the casing to blow up. PA1 low toxicity of the gas and aerosol mixture; PA1 low temperature of the gas and aerosol mixture, while having high fire extinguishing efficiency. PA1 reduction of toxicity of the fire extinguishing gas and aerosol mixture that is fed to a space being protected, primarily by lowering the level of NO, CO, NH.sub.3, HCN and by lowering the content of aerosol particles of a size smaller than 1 .mu.m. PA1 Lowering the temperature of the fire extinguishing gas and aerosol mixture that is fed to a space being protected to rule out the presence of flames and sparks in the area, thus enhancing the fire extinguishing efficiency of the gas and aerosol mixture. PA1 constant temperature profile during burning (from 460.degree. C. in the condensed phase to 750.degree. C. at the hottest point of the flame); PA1 constant gas phase-to-aerosol ratio of 30:70, with the pass part of the aerosol particles of a size from 1 to 2 .mu.m being no less than 70%; PA1 stability of the chemical composition and concentration of the gas phase that is released during burning of the composition. PA1 heat transfer from the fire flames; PA1 deactivation of the active atoms and radicals of the fire flames on the surface of the highly active solid aerosol particles. Fire is extinguished in a few seconds, and there is no harmful effect on living organisms and environment. PA1 the process of the complete catalytic oxidation of the products of incomplete combustion is carried out: PA1 The use of the above-described pyrotechnic composition that ensures a stable temperature distribution and gas phase composition, which contains dicyandiamide as a gas and aerosol former, a polycondensate of formaldehyde with phenol as a combustible binder, and potassium nitrate as an oxidizer. The gas and aerosol former, the combustible binder, and the oxidizer each consist of two fractions, respectively: 40 to 80 .mu.m and 7 to 15 .mu.m in the mass ratio of 80:20, 70 to 120 .mu.m and 10 to 25 .mu.m in the mass ratio of 70:30, and 15 to 25 .mu.m and 1 to 7 .mu.m in the mass ratio of 25:75, with the following proportioning of the components (% by mass): PA1 The use of a solid coolant selected from the group of silica gel, aluminosilicate (zeolite). PA1 lowering the toxicity of the fire-extinguishing gas and aerosol mixture owing to the high-efficiency of the complete oxidation of the combustion products; PA1 simplified construction of the apparatus with higher fire-extinguishing efficiency and safety during use.
Russian Patent 2 087 170 presents a method for fire extinguishing in spaces wherein solid fuel is added to combustion products, which are completely oxidized and cooled before being fed to a space being protected. The complete oxidation occurs in a jet flow, with an oxidizer being oxygen of the ambient air or other oxidizer formers, which are fed under pressure into a generator. Cooling of the combustion products occurs through heat exchange between the walls of a heat exchanger and a fluid coolant similar to the cooling system of a motor vehicle internal combustion engine.
This method has the following main disadvantages:
In case an oxidizer is to be supplied from a special pressurized gas bottle, which is required in some applications, the construction of the apparatus becomes more expensive.
Among other disadvantages are the following:
The closest prior art is described in Russian Patent Application 94 002 970 which presents a method for fire extinguishing in enclosed spaces comprising the following steps:
Through all the steps, catalysts of oxidation of the combustion products are used, which are selected from metals including nickel, cobalt, iron, manganese, chromium, aluminum, magnesium, copper, platinum, silver, their oxides and or peroxides, salts, as well as their alloys and mixtures. The aerosol-forming composition, the heat-absorbent filling, and the oxidizer filling may be mixed with the above-mentioned catalysts or may be included in the respective compositions. Oxidizers are selected from among the following substances: ammonium nitrate, potassium nitrate, sodium nitrate, calcium nitrate, barium nitrate, strontium nitrate, ammonium perchlorate, potassium perchlorate, sodium perchlorate, and their mixtures.
The main disadvantage of this method is inefficient application of the oxidation catalysts. This results in the process of complete oxidation of the combustion products having a low efficiency, which, in turn, causes a higher level of toxic gases in the gas and aerosol mixture.
The low efficiency of the complete oxidation is explained by the following factors:
Therefore, the state of the art does not allow the required properties to be obtained simultaneously, namely: